The present invention relates generally to systems and techniques for monitoring heater systems and, more particularly, to systems and techniques for determining current levels and ground fault conditions for multiple control loops of a heater system, such as a heat tracing system.
The monitoring of heating and temperature conditions of process system equipment, such as tanks and pipes, is a common industrial practice that may have many applications. For example, heating may be required to maintain heavy oils or resins at a certain viscosity to allow such fluids to be readily pumped through tanks and pipes. Heating also may prevent crystalline precipitation or freezing during a process, or may simply facilitate the process itself. Typically, monitoring and controlling the heating of process system equipment involves the use of heating elements and sensors.
An electrical heat tracing system is one example of a heating system that may be used for protection from freezing, maintenance of an adequate process temperature, and/or de-icing of structures (e.g., tanks, pipes, roofs, gutters). FIG. 1 illustrates a schematic of a conventional heat tracing system 10. As shown, the heat tracing system 10 include a controller 12, a plurality of heater loads 14a-d (e.g., heat trace or heat strips), a plurality of control devices 16a-d, and a plurality of sensors 18a-d, 20a-d. A power bus 22 branches into individual connections 24a-d for distributing power to each of the heater loads 14a-d. Each heater loads 14a-d may, in turn, be attached to component needing heat such as a chamber, tank, vessel or pipe.
Each individual branch 24a-d of the power bus 22 connecting to the heater loads 14a-d includes a control device 16a-d and sensors 18a-d, 20a-d. The control devices 16a-d are switches that disconnect the flow of power to the heater loads 14a-d from the power bus 22 when actuated by the controller 12.
The sensors typically include current monitors 18a-d and ground fault detectors 20a-d. The current monitors 18a-d detect changes in the current supplied to the heater loads 14a-d and provide control signals to the controller 12 via control lines 28a-d. The controller 12 determines when the current supplied to any of the heater loads 14a-d falls outside set parameters or meets an alarm condition. The controller 12 actuates the associated control device 16a-d and breaks the flow of power to the heater load 14a-d with the deviation in the current supply. The controller 12 receives separate signals from each of the current monitors 18a-d and individually shuts off power to the heater loads 14a-d when an alarm condition is indicated.
The ground fault detectors 20a-d detect leakage in current due to a ground fault in the heater loads 14a-d. A ground fault in the heating cable involves leakage of current at some location along its length. A ground fault may occur in a system due to mechanical damage, flooding, cable chaffing or corrosion. In the event that one of the heater loads 14a-d is grounded, the ground fault detector 20a-d associated with the grounded heater load 14a-d provides a signal to the controller 12 via one of the control lines 30a-d. The controller 12, in turn, actuates the associated control device 16a-d and breaks the flow of power to the grounded heater load 14a-d. The controller 12 receives separate signals from each of the ground fault detectors 20a-d and individually shuts off power to the heater loads 14a-d when a ground fault condition is indicated.
As depicted in FIG. 1, each control loop of the conventional heat tracing system 10 is supported by many components including current monitors 18a-d, ground fault detector 20a-d and control devices 16a-d. Given that a heat tracing system may have upwards of twenty-four separate control loops, a large number of sensors and detectors employed throughout the heater loads is required. Connecting the controller to the various sensors and detectors requires a great deal of installation and expense. Furthermore, the controller requires numerous inputs and outputs to properly connect to all of the sensors and requires the necessary processing ability to handle signals from the numerous sensors and detectors.
Accordingly, there is a need for monitoring heater systems in a way that overcomes, or at least reduces the effects of, one or more of the problems set forth above.
In one general aspect, a monitoring system includes a sensor that detects operating conditions in a plurality of control loops of a heater system and generates signals corresponding to the detected operating conditions. The monitoring system also includes a controller that receives the signals from the sensor and determines whether the signals indicate the presence of an alarm condition in one or more of the control loops. The controller is configured to temporarily disconnect power to the plurality of control loops when it is determined that an alarm condition is present, determine whether the alarm condition is present in an individual connector loop, and reconnect power to only those control loops in which the alarm condition is not present.
Implementations may include one or more of the following features. For example, the alarm condition may include a deviation in current level and/or a ground fault condition. The sensor may include a current monitor and/or a ground fault detector. The sensor may detect an ampere level of power supplied to the plurality of control loops, and the controller may compare the ampere level against a high setpoint and a low setpoint. The controller may include a database for storing data indicating an alarm condition in one or more control loops.
The monitoring system may include a plurality of control devices. Each control device may be configured to disconnect power to an individual control loop when actuated by the controller. Each control device may include an isolation contactor, a relay, and/or a circuit breaker.
The monitoring system also may include a first sensor and a second senor. The senor may first sensor may detect first operating conditions in the plurality of control loops and the second sensor may detect second operating conditions in the plurality of control loops. The controller may receive the signals from the first sensor and the second sensor and temporarily disconnect power to the plurality of control loops when it is determined that at least one of a first alarm condition and a second alarm condition is present in one or more of the control loops. The first sensor may include a current monitor and the second sensor may include a ground fault detector.
The heater system may include a power bus connecting the sensor and the plurality of control loops. The power bus may have a plurality of braches with each branch distributing power to an individual control loop. The sensor may be located on the power bus before the separation of the power bus into the plurality of branches.
In another general aspect, a monitoring method includes determining whether signals received from a sensor indicate the presence of an alarm condition in one or more control loops. The sensor detects operating conditions in a plurality of control loops of a heater system and generates signals corresponding to the detected operating conditions. The monitoring method also includes temporarily disconnecting power to the plurality of control loops when it is determined that an alarm condition is present, determining whether the alarm condition is present in an individual connector loop, and reconnecting power to only those control loops in which the alarm condition is not present.
Implementations may include one or more of the following features. For example, the alarm condition may include a deviation in current level and/or a ground fault condition. Determining whether the alarm condition is present in an individual connector loop may involve sending a test signal for detection by the sensor and/or reconnecting an individual control loop to a power bus and monitoring the power bus for the alarm condition. Monitoring the power bus for the alarm condition may involve detecting whether the power bus meets a specified parameter, for instance, by comparing an ampere level of the power bus against setpoint to determine if deviation has occurred in the individually reconnected control loop. The specified parameter may be indicative of current leakage due to a ground fault condition in the individually reconnected control loop.
In another general aspect, a computer program stored on a computer-readable medium includes a first routine for determining whether signals received from a sensor indicate the presence of an alarm condition in one or more control loops. The sensor detects operating conditions in a plurality of control loops of a heater system and generates signals corresponding to the detected operating conditions. The computer program also includes a second routine for temporarily disconnecting power to the plurality of control loops when it is determined that an alarm condition is present, a third routine for determining whether the alarm condition is present in an individual connector loop, and a fourth routine for reconnecting power to only those control loops in which the alarm condition is not present.
Implementations may include one or more of the following features. For example, the computer-readable medium may include a device, disk, and/or propagated signal. The alarm condition may include a deviation in current level and/or a ground fault condition. The computer program may include a routine for isolating one or more control loops having the alarm condition and/or a routine for storing data from the sensor.
Other features and advantages will be apparent from the following description, including the drawings, and from the claims.